This invention pertains to submersible, electric-motor driven liquid pumps, and to means for liquid-cooling of the electric motors thereof, and in particular to such a motor and cooling means therefor which offers greatly improved motor coolant circulation and cooling efficiency.
A common type of pump is the so-called submersible one in which the pump and the electric motor therefor comprise a unit which is submersed in the pumped liquid. Such a motor normally obtains its cooling directly from the surrounding, pumped liquid. If, however, the level of the liquid decreases, so that the motor is surrounded by air, the cooling of the motor way be insufficient. Consequently, it is known to provide an internal cooling system, for the motor, which uses the pumped liquid for the purpose. An example of such an internal cooling system is disclosed in the Swedish patent No. 367 465.
As the pumped liquid often contains pollutants, said patent teaches the use of a narrow slot, arranged between the impeller of the pump and the pump housing, through which comparatively clean liquid is conducted into the cooling water area between the pump and the motor. Ancillary vanes, formed atop the impeller, cause the cooling water to circulate. The aforesaid slot prevents solid pollutants from entering the aforesaid area and, consequently, diminishes the likelihood of a clogging of cooling channels about the motor.
Further, the cited patent discloses the use of vanes, within the cooling jacket which houses the motor, for directing the cooling liquid upwardly, along the motor, to effect cooling of the entire motor.
Because of the development towards larger and more powerful motors, the demand for good cooling of such has been increased. Yet, cooling therefor available by the known weans is not always adequate. Problems arise due to the fact that is is difficult for the cooling liquid to reach upper portions of the motor as solid pollutants accrete in the cooling-liquid passages. Additionally, motors are often operated at slow speeds and, consequently, they can not effect a sufficient cooling liquid circulation without large, energy-demanding ancillary vanes. To solve the problem and provide enhanced, cooling liquid circulation, it has been proposed to convey cooling liquid to the top of the motor in separate, outwardly-arranged conduits. By this arrangement, the cooling liquid will flow down, between the stator housing of the motor and the surrounding cooling jacket, The main disadvantage with this is that these external conduits are expensive and readily subject to damage during rough handling of the motor-pump.
An alternative solution, which has been tested, is to arrange the conduits for the cooling liquid within the motor housing. Then, to insure that the conduits will not disturb the circular flow about the motor stator housing, the latter is provided with longitudinal ridges or recesses in which the conduits are nested. Such ridges or recesses, however, disturb the symmetry and require that the stator housing have considerably thicker and stronger wall material to sustain the pressure loading thereof. Tests have established that a stator housing designed in this manner requires wall material three times thicker than that required by a fully circular stator housing, to be able to withstand a same, internal pressure.